The present invention relates to a safety switch for monitoring movable protection devices having a switching member with a reading head and having an actuating element movable relative to the reading head and co-operating with the reading head in a contactless manner.
Movable protection devices in the configuration of doors and coverings on machines and processing plants are monitored with safety switches. The protection devices separate persons and machines form one another for the protection of both. For this purpose, during opening of doors or coverings, the safety switch must safely interrupt one or more current circuits and hold them disconnected until the protection device is closed again.
Electrical/mechanical safety switches for this purpose have a switching member connected with the stationary part of the protection device, into which can be introduced a separate operation control arrangement connected with the movable protection device. The separate operation control arrangement in the introduced state closes the switch contacts. When the protection device is opened, in other words without the operation control arrangement being introduced, the switch contacts are forcibly opened by a form-locking arrangement transferring the energy.
In those cases of use in which electrical/mechanical safety switches cannot be used because the environment is of extraordinary hygienic or other environmental conditions (foodstuffs processing, purification plants), operation control s with several permanent magnets are used. The magnets interact with reading heads without contact. Coils are provided in the reading heads. For safety reasons, at least three magnets must be provided. As opposed to electrical/mechanical safety switches, magnetic safety switches are considerably more sensitive in the case of vibrations. Additionally, when a breakdown occurs the preferred reaction is that the switch not be opened.
Objects of the present invention are to provide an improved safety switch for movable protection devices. These objects are attained according to the present invention by a safety switch for monitoring movable protection devices, comprising a switching member having at least one reading head, and an operation actuating element movable relative to the reading head and interacting with the reading head without contacting the reading head. The actuating element has an inductive reactance for interacting with the reading head and an electronic code in a first storage specifically identifying the actuating element. An evaluation device is connected at an output of the reading head, includes an electronic code in at least two second storages specifically identifying one of the reading head and the switching member, and includes at least two sets of components for analyzing and evaluating signals from the reading head.
Since the actuating element for interaction with the reading head has an inductive reactance, permanent magnets of any sort are no longer required in the operation control mechanism. The safety switch is thus insensitive to vibrations. At the same time, the problem of the magnets having an extended operation range, creating a disruptive effect when the mechanism is moved to either side, is also overcome. Upon breakdown of the inductive reactance of the reading head, no existence of an actuating element can be established. Thus, the safety switch then switches over into the safe state, in other words into opened state. When that occurs an inductive reactance offers greater safety than the device using three permanent magnets. As a result of the relatively extensive mechanical tolerances between actuating element and reading head, use of the safety switch according to the present invention is possible even in the case of heavy protection doors.
The reading head likewise advantageously has an inductive reactance which interacts over a magnetic alternating field with the inductive reactance of the actuating element. The two inductive reactances then form a transformer. This transformer can be operated under the safety technology principle of dynamic signal transmission. This allows for operation even with very high safety requirements using a structure having one single channel. The production of the reading head is greatly simplified and is of considerably lower cost.
It is especially advantageous when the actuating element picks up or absorbs its energy for operation from this magnetic alternating field. No separate voltage supply is required for the actuating element. Thus, the probability of a technical breakdown of the inductive reactance (with the resultant switching of the safety switch setting into the opened state) is greatly decreased. Also, the corresponding maintenance costs of the operation control are greatly decreased.
It is advantageous when the actuating element includes an electronic coding in a storage area, which specifically identifies the actuating element. Each actuating element is then a unique element. Any manipulations of the safety switch with the aid of another actuating element are precluded. At the same time, digital analysis/evaluation is possible instead of analog analysis/evaluation over a frequency shift. Similar actuating elements are used for identification systems in which movable ramming or tamping tools or ramming or tamping tool pallets carry such actuating element, which is detected by graphics- or registration-reading heads, and thereafter, is suitably programmed in order to supply instructions and/or feedback to a machine for the movement or transport of these parts.
When an analysis and evaluation device is series-connected at the outlet side on the reading head, which reading head includes an electronic coding in at least one further storage, specifically identifying the reading head or the switching member, each safety switch is also a unique element. In combination with a specifically identifiable actuating element, each individual safety switch reacts only to the signal from one single actuating element. For this purpose it is preferred that a comparison device be provided within the analysis/evaluation device. The comparison device compares the coding coming out of the actuating element with the stored coding of the same. Preferably, the coding coming form the actuating element for inducement of the operation of the reading head is read and picked up by the latter. Similar systems which are called transponders can also be used for the electronic automatic travel stop devices of automobiles, for example, in connection with ignition keys.
Because of the high safety level of the actuating element-reading head-system, it suffices for this arrangement to be configured with only one channel. On account of high sensitivity of the analysis/evaluation electronics, it is advantageous for the information flow to occur in two channels in the analysis/evaluation device. This is attained when at least twice as many parts of the analyzing/evaluating device, which are competent and authorized for the customary analysis/evaluation of the signal picked up from the reading head, are present.
Using a reliable technique, the safety switch has a key-like operation control which can be introduced into the housing of the switching member. One arrangement for use of the present invention is when the actuating element is provided mounted on the operation control, while correspondingly the reading head is provided within the housing of the switching member. An interchangeable arrangement however would also be conceivable. With use of known technology, the operation control is interlocked by use of a ramming or tamping rod. Another use of the present invention is with the actuating element mounted on the ramming or tamping rod, and with the reading head arranged within the housing of the switching member. Also, the arrangements could be suitably interchanged.
Because of the cost of material, it can be advantageous that the operating control be configured of plastic rather than metal. One advantageous protection against fault or error function as a result of a break of the operation control is obtained when one winding of the inductive reactance of the actuating element extends over almost the entire length of the operation control.
Other objects, advantages and salient features of the present invention will become apparent form the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.